Such covers or roofs are typically installed on the furnace vessel and remain in place during the entire operation, including the tilting movements of the vessel for tapping and slagging. In certain phases of the operation, for example, when the vessel is being charged, the cover or roof is lifted from the vessel and swung to the side. Thus a furnace roof is subjected to lifting, swiveling, and tilting during the operation of the furnace.
Particular importance is accorded to the supply and discharge of coolant to and from the spray-cooled roofs when these are in various positions in the cycle of operation. The U.S. Pat. No. 4,715,042 discloses a spray-cooled cover, for which the coolant is drawn off by means of venturi pumps. In practical operations, this type of pump has been incapable of drawing off very large amounts of coolant. In certain instances, water collects in the cover so that, instead of spray cooling, normal water cooling exists, leading to the negative results of overheating of the roof elements in the affected area. In addition, this roof uses large quantities of water.
The U.S. Pat. No. 4,789,991 of Mannesmann AG discloses a spray-cooled roof, for which disc pumps are used, which pumps are able to draw off larger amounts of water. Moreover, even after such pumps run dry, that is, when there is a break in the continuity of the water on the suction side, they are suitable nevertheless for starting up operations once again. These pumps are connected by means of hoses with the spray-cooled cover and thus permit the roof to be tilted. However for swiveling the cover, it is necessary to disconnect these hoses from the cover by means of rapid action (quick-disconnect) hose couplings. It should be mentioned that, for the known methods of supplying and discharging coolant, not only are pumps required for the spray water but separately operated pumps are also required for drawing off the coolant.